We're at the stage out in time with pretty much all the models where they usually like to show everything but the truth when it comes to trough geometry... but even the ensembles are leaning more toward the idea of the operational models where the lead jet energy in the Friday/Saturday trough gets pulled north, and it stretches the trough and the base of it waits until Saturday afternoon/night to swing across. Interestingly, while that would decrease the chances of a major outbreak if it were to happen, it would actually probably increase the chances of there being a tornado event actually verifying instead of the wave being a complete dud, because then the lead impulse acts as the primer wave, and you get a full day of then absolutely guaranteed return flow regardless of what the ridge and wavelengths are doing out in the Atlantic to the east. The trough geometry isn't optimal, but you still get a low-level air mass supportive of severe weather with low-level and deep-layer wind fields supportive of some caliber of a tornado threat (linear, cellular, or mixed would be tbd). It just wouldn't be the headliner national-news-story type event this was trying to present itself as at one point. The main surface low positioning would still be well north, but as long as you're still getting pressure falls to back the low-level winds ahead of the front and height falls aloft, that doesn't matter. With the 11/10/2002 tornado outbreak, the main surface low was moving into southern Canada and away from the outbreak area that morning. In the 3/3/1966 "Candlestick Park" F5 event near Jackson, MS, the synoptic surface low was in central South Dakota. It's actually the same low pressure that caused the big Fargo, ND blizzard that led to the infamous photo of the guy standing on the snow drift that came up to the top of telegraph poles. Surface low position doesn't matter if you still have a catalyst to have pressure falls and back low-level winds ahead of the front and you still have large scale ascent aloft.
But we're now in that funky 4-7 day window where both operational models and ensembles sometimes do all kinds of funky things with trough evolution and geometry before settling onto what will be reality about the 3-4 day timeframe. A lot of people don't remember this because it was touted as a significant severe weather threat in general from a week out, but the models did not show a trough geometry favorable for a discrete supercell swarm with 4/27/11 until about the 00z model cycle the night the Day 3 MDT was issued. You can go back and look, and it was even talked about in real time in the medium range days prior in that thread. The trough geometry was more disjointed and meridional and supported something more along the lines of a repeat of April 4th but with more tornadoes. It wasn't until the 00z model cycle leading into the Day 3 MDT issuance that we suddenly had a shift toward a broad-based low amplitude trough geometry. Now, that is NOT being said to make even the absolute slightest comparison between that threat and this potential one, but I'm saying that to show the point that, even with slam dunk home run type setups like that, the global models and even their ensembles still do funky things with trough evolution and geometry in the medium range. The main takeaway from that message is: there's still a lot we just don't know yet, and even if what we're currently being presented ends up being reality, we don't have a way of having confidence in that yet.
